Magnetic memory cell construction

ABSTRACT

A magnetic tunnel junction cell having a free layer, a ferromagnetic pinned layer, and a barrier layer therebetween. The free layer has a central ferromagnetic portion and a stabilizing portion radially proximate the central ferromagnetic portion. The construction can be used for both in-plane magnetic memory cells where the magnetization orientation of the magnetic layer is in the stack film plane and out-of-plane magnetic memory cells where the magnetization orientation of the magnetic layer is out of the stack film plane, e.g., perpendicular to the stack plane.

RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationNo. 61/087,207, filed on Aug. 8, 2008. The entire disclosure ofapplication No. 61/087,207 is incorporated herein by reference.

BACKGROUND

Spin torque transfer technology, also referred to as spin electronics,combines semiconductor technology and magnetics, and is a more recentdevelopment. In spin electronics, the spin of an electron, rather thanthe charge, is used to indicate the presence of digital information. Thedigital information or data, represented as a “0” or “1”, is storable inthe alignment of magnetic moments within a magnetic element. Theresistance of the magnetic element depends on the moment's alignment ororientation. The stored state is read from the element by detecting thecomponent's resistive state.

The magnetic element, in general, includes a ferromagnetic pinned layerand a ferromagnetic free layer, each having a magnetization orientationthat defines the resistance of the overall magnetic element. Such anelement is generally referred to as a “spin tunneling junction,”“magnetic tunnel junction”, “magnetic tunnel junction cell”, and thelike. When the magnetization orientations of the free layer and pinnedlayer are parallel, the resistance of the element is low. When themagnetization orientations of the free layer and the pinned layer areantiparallel, the resistance of the element is high.

At least because of their small size, it is desirous to use magnetictunnel junction elements in many applications. However, their small sizealso creates issues.

One of the primary issues preventing magnetic tunnel junction elementsfrom replacing other memory elements is the memory cell-to-celldistribution. Significant variations from cell-to-cell exist formagnetic tunnel junction cells. In writing to those cells, the result isa switching field distribution, rather than a constant value; in readingback from those cells, there is variation in resistance and noise.Additionally, thermal stability and stray field sensitivity are issues.Various attempts have been made to provide more stabile, more consistentmagnetic tunnel junction cells and memory arrays. There is always roomfor improvement.

BRIEF SUMMARY

The present disclosure relates to magnetic tunnel junction cells thathave a free layer composed of a central ferromagnetic portion, having areadily switchable magnetization orientation, and a stabilizing portion,which stabilizes the magnetization configuration of the centralferromagnetic portion. If the stabilizing portion comprises anantiferromagnetic material, the stabilization is via exchange couplingat the interface between the central ferromagnetic portion and thestabilizing portion. If the stabilizing portion comprises aferromagnetic portion, a spacer layer is present between the centralferromagnetic portion and the stabilizing portion, and the stabilizationis via magnetostatic coupling across the spacer layer.

In one particular embodiment, this disclosure describes a magnetictunnel junction cell having a free layer, a ferromagnetic pinned layer,and a barrier layer therebetween. The free layer has a centralferromagnetic portion and a stabilizing portion radially proximate thecentral ferromagnetic portion.

In another particular embodiment, this disclosure describes a method formaking a magnetic tunnel junction cell. The method includes providing,in order, a bottom electrode, a ferromagnetic pinned layer, a barrierlayer and a ferromagnetic free precursor layer. A free layer is formedfrom the precursor layer and a stabilizing material is deposited overthe free layer. The stabilizing material is pattered to form astabilizing ring radially proximate to the free layer. The free layer isexposed by removing at least a portion of the stabilization material. Atop electrode is provided over the exposed free layer.

Additional embodiments of magnetic tunnel junction cells and memoryunits are disclosed, as well as memory arrays including the units, andmethods of making and using the cells.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1A is a side view cross-sectional diagram of an illustrativemagnetic tunnel junction cell with in-plane magnetization orientation;FIG. 1B is a side view cross-sectional diagram of an illustrativeperpendicular anisotropy magnetic tunnel junction cell with out-of-planemagnetization orientation;

FIG. 2 is a side view cross-sectional diagram of a first embodiment of amagnetic tunnel junction cell of this disclosure; FIG. 2A is a top viewof the free layer of the magnetic tunnel junction cell of FIG. 2;

FIG. 3 is a side view cross-sectional diagram of a second embodiment ofa magnetic tunnel junction cell of this disclosure;

FIG. 4 is a side view cross-sectional diagram of a third embodiment of amagnetic tunnel junction cell of this disclosure; FIG. 4A is a top viewof the free layer of the magnetic tunnel junction cell of FIG. 4;

FIG. 5 is a side view cross-sectional diagram of a fourth embodiment ofa magnetic tunnel junction cell of this disclosure;

FIG. 6 is a side view cross-sectional diagram of a fifth embodiment of amagnetic tunnel junction cell of this disclosure;

FIG. 7 is a side view cross-sectional diagram of a sixth embodiment of amagnetic tunnel junction cell of this disclosure;

FIGS. 8A though 8G step-wise illustrate a method for making a magnetictunnel junction cell of this disclosure; and

FIG. 9 is a flow chart of a method for making a magnetic tunnel junctioncell of this disclosure.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION

This disclosure is directed to memory cells and methods of making thosecells. The devices (e.g., magnetic tunnel junction cells) of thisdisclosure have a free layer that has a ferromagnetic center portion andan antiferromagnetic or a ferromagnetic portion radially around thecenter portion. In some embodiments, a spacer layer is positionedbetween the ferromagnetic center portion and the ferromagnetic portion.The antiferromagnetic portion stabilizes the magnetization orientationof the free layer. The construction can be used for both in-planemagnetic memory cells where the magnetization orientation of themagnetic layer is in the stack film plane and out-of-plane magneticmemory cells where the magnetization orientation of the magnetic layeris out of the stack film plane, e.g., perpendicular to the stack plane.

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.The definitions provided herein are to facilitate understanding ofcertain terms used frequently herein and are not meant to limit thescope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

The present disclosure relates to magnetic tunnel junction cells andmethods of making magnetic tunnel junction cells. The magnetic tunneljunction cells of this disclosure include a radially protective layerextending proximate at least the ferromagnetic free layer of the cell.While the present disclosure is not so limited, an appreciation ofvarious aspects of the disclosure will be gained through a discussion ofthe examples provided below.

FIG. 1A is a cross-sectional schematic diagram of a generic magnetictunnel junction cell 10A that includes a relatively soft ferromagneticfree layer 12A and a ferromagnetic reference (i.e., fixed or pinned)layer 14A. Ferromagnetic free layer 12A and ferromagnetic pinned layer14A are separated by an oxide barrier layer 13A or non-magnetic tunnelbarrier. Note that other layers, such as seed or capping layers, are notdepicted for clarity.

Ferromagnetic layers 12A, 14A may be made of any useful ferromagnetic(FM) material such as, for example, Fe, Co or Ni and alloys thereof,such as NiFe and CoFe. Ternary alloys, such as CoFeB, may beparticularly useful because of their lower moment and high polarizationratio, which are desirable for the spin-current switch. Either or bothof free layer 12A and pinned layer 14A may be either a single layer oran unbalanced synthetic antiferromagnetic (SAF) coupled structure, i.e.,two ferromagnetic sublayers separated by a metallic spacer, such as Ruor Cu, with the magnetization orientations of the sublayers in oppositedirections to provide a net magnetization. The magnetization orientationof ferromagnetic free layer 12A is more readily switchable than themagnetization orientation of ferromagnetic pinned layer 14A; the twoopposing magnetization arrows in free layer 12A represent readilyswitchable magnetization orientation. Barrier layer 13A may be made ofan electrically insulating material such as, for example an oxidematerial (e.g., Al₂O₃, TiO_(x) or MgO). Other suitable materials mayalso be used. Barrier layer 13A could optionally be patterned with freelayer 12A or with pinned layer 14A, depending on process feasibility anddevice reliability.

The following are various specific examples of magnetic tunnel junctioncells 10A. In some embodiments of magnetic tunnel junction cell 10A,oxide barrier layer 13A includes Ta₂O₅ (for example, at a thickness ofabout 0.5 to 1 nanometer) and ferromagnetic free layer 12A and aferromagnetic pinned layer 14A include NiFe, CoFe, or Co. In otherembodiments of magnetic tunnel junction cell 10, barrier layer 13Aincludes GaAs (for example, at a thickness of about 5 to 15 nanometers)and ferromagnetic free layer 12A and ferromagnetic pinned layer 14Ainclude Fe. In yet other embodiments of magnetic tunnel junction cell10A, barrier layer 13A includes Al₂O₃ (for example, a few nanometersthick) and ferromagnetic free layer 12A and ferromagnetic pinned layer14A include NiFe, CoFe, or Co.

A first electrode 18A is in electrical contact with ferromagnetic freelayer 12A and a second electrode 19A is in electrical contact withferromagnetic pinned layer 14A. Electrodes 18A, 19A electrically connectferromagnetic layers 12A, 14A to a control circuit providing read andwrite currents through layers 12A, 14A. The resistance across magnetictunnel junction cell 10 is determined by the relative orientation of themagnetization vectors or magnetization orientations of ferromagneticlayers 12A, 14A. The magnetization direction of ferromagnetic pinnedlayer 14A is pinned in a predetermined direction while the magnetizationdirection of ferromagnetic free layer 12A is free to rotate under theinfluence of spin torque. Pinning of ferromagnetic pinned layer 14A maybe achieved through, e.g., the use of exchange bias with anantiferromagnetically ordered material (AFM) such as PtMn, IrMn, andothers.

In some embodiments, magnetic tunnel junction cell 10A is in the lowresistance state where the magnetization orientation of ferromagneticfree layer 12A is parallel and in the same direction of themagnetization orientation of ferromagnetic pinned layer 14A. This istermed the low resistance state or “0” data state. In other embodiments,magnetic tunnel junction cell 10A is in the high resistance state wherethe magnetization orientation of ferromagnetic free layer 12A isanti-parallel and in the opposite direction of the magnetizationorientation of ferromagnetic pinned layer 14A. This is termed the highresistance state or “1” data state.

Switching the resistance state and hence the data state of magnetictunnel junction cell 10A via spin-transfer occurs when a current,passing through a magnetic layer of magnetic tunnel junction cell 10A,becomes spin polarized and imparts a spin torque on free layer 12A ofmagnetic tunnel junction cell 10A. When a sufficient spin torque isapplied to free layer 12A, the magnetization orientation of free layer12A can be switched between two opposite directions and accordingly,magnetic tunnel junction cell 10A can be switched between the parallelstate (i.e., low resistance state or “0” data state) and anti-parallelstate (i.e., high resistance state or “1” data state).

As shown in FIG. 1A and discussed above, a generic magnetic tunneljunction cell has three main parts: ferromagnetic free layer 12A,barrier layer 13A and ferromagnetic reference or pinned layer 14A. Freelayer 12A is where data or bit information is stored when the deviceoperates under “read”, or overwritten when the device operates under“write”. Each ferromagnetic layer 12A, 14A acts as a “spin filter” whencell 10A writes with “0” or “1” as the switching current passes throughin opposite directions to alter magnetization of free layer 12A.

The magnetization orientations of free layer 12A and pinned layer 14A ofmagnetic tunnel junction cell 10A are in the plane of the layers, orin-plane. FIG. 1B illustrates an alternate embodiment of a magnetictunnel junction cell that has the magnetization orientations of the freelayer and the pinned layer perpendicular to the plane of the layers, orout-of-plane.

Similar to magnetic tunnel junction cell 10A of FIG. 1A, magnetic tunneljunction cell 10B of FIG. 1B has relatively soft ferromagnetic freelayer 12B and a ferromagnetic reference (i.e., fixed or pinned) layer14B separated by an oxide barrier layer 13B or non-magnetic tunnelbarrier. Pinned layer 14B can be a single layer with large coercivity ora layer pinned by a pinning layer, or a synthetic antiferromagnetic(SAF) trilayer, or a SAF pinned by a pinning layer. A first electrode18B is in electrical contact with ferromagnetic free layer 12B and asecond electrode 19B is in electrical contact with ferromagnetic pinnedlayer 14B. Other layers, such as seed or capping layers, are notdepicted for clarity. Electrodes 18B, 19B electrically connectferromagnetic layers 12B, 14B to a control circuit providing read andwrite currents through layers 12B, 14B. The various elements of cell 10Bare similar to the element of cell 10A, described above, except that themagnetization orientations of layers 12B, 14B are oriented perpendicularto the layer extension rather than in the layer plane.

Free layer 12B and pinned layer 14B each have a magnetizationorientation associated therewith, illustrated in FIG. 1B, where twoopposing magnetization arrows represent a readily switchablemagnetization orientation. In some embodiments, magnetic tunnel junctioncell 10B is in the low resistance state or “0” data state where themagnetization orientation of free layer 12B is in the same direction ofthe magnetization orientation of pinned layer 14B. In other embodiments,magnetic tunnel junction cell 10B is in the high resistance state or “1”data state where the magnetization orientation of free layer 12B is inthe opposite direction of the magnetization orientation of pinned layer14B.

Similar to cell 10A of FIG. 1A, switching the resistance state and hencethe data state of magnetic tunnel junction cell 10B via spin-transferoccurs when a current, passing through a magnetic layer of magnetictunnel junction cell 10B, becomes spin polarized and imparts a spintorque on free layer 12B. When a sufficient spin torque is applied tofree layer 12B, the magnetization orientation of free layer 12B can beswitched between two opposite directions and accordingly, magnetictunnel junction cell 10B can be switched between the low resistancestate or “0” data state and the high resistance state or “1” data state.

The previous discussion directed to cell 10A of FIG. 1A and cell 10B ofFIG. 1B applies, in general, to the magnetic tunnel junction cellsdescribed below. The various elements of the tunnel junctions describedbelow are similar to and have the same or similar properties andfeatures as the corresponding elements of cells 10A, 10B describedabove, unless indicated otherwise.

FIG. 2 is a cross-sectional schematic diagram of a magnetic tunneljunction cell 20 that includes a soft ferromagnetic free layer 22, aferromagnetic reference (i.e., pinned) layer 24, and anantiferromagnetic pinning layer 26. Ferromagnetic layers 22, 24 may bemade of any useful ferromagnetic (FM) material, such as described above.Pinned layer 24 can be a single layer or a synthetic antiferromagnetic(SAF) trilayer. Pinning layer 26 is an antiferromagnetically orderedmaterial such as PtMn, IrMn, and others. Ferromagnetic free layer 22 andferromagnetic pinned layer 24, each which have a magnetizationorientation associated therewith, are separated by an oxide barrierlayer 23 or non-magnetic tunnel barrier. In FIG. 2, the magnetizationorientations of free layer 22 and pinned layer 24 are shown as parallel,although it is well understood that these orientations could beantiparallel. The magnetization orientation of pinned layer 24 is pinnedby antiferromagnetic pinning layer 26, or in other embodiments, may be afixed layer without pinning but with a high coercivity to stabilizeitself. For magnetic tunnel junction cell 20, the magnetizationorientations of free layer 22 and pinned layer 24 are in the plane ofthe layers, or in-plane. Note that other layers, such as seed or cappinglayers, are not depicted for clarity. A first electrode 28 is inelectrical contact with ferromagnetic free layer 22 and a secondelectrode 29 is in electrical contact with ferromagnetic pinned layer 24via antiferromagnetic pinning layer 26.

In accordance with this disclosure, free layer 22 has a ferromagneticcentral portion 25 and a stabilizing portion 27 positioned radiallyproximate to central portion 25. In this embodiment, stabilizing portion27 is an antiferromagnetic (AFM) material; PtMn (e.g., Pt₁₀Mn₉₀), FeMn,IrMn, NiMn, and CrMnPt are suitable materials for antiferromagneticstabilizing portion 27. In some embodiments, stabilizing portion 27 isan antiferromagnetic electrically conducting material, whereas in otherembodiments, stabilizing portion 27 is an antiferromagnetic electricallyinsulating material (NiO is one suitable such material). Central portion25 has a smaller size (e.g., diameter) than the corresponding pinnedlayer 24; together, central portion 25 and stabilizing portion 27 havethe same or similar size as the corresponding pinned layer 24. Electrode28 is smaller than free layer 22 and does not extend to the edges offree layer 22; in the illustrated embodiment, electrode 28 is smallerthan central portion 25; this construction inhibits and preferablyprevents current from flow from electrode 28 to stabilization portion27.

As seen in FIG. 2 and in FIG. 2A, central portion 25 and stabilizingportion 27 meet at an interface 27A. In this embodiment, withstabilizing portion 27 being an antiferromagnetic material, exchangecoupling occurs at interface 27A between stabilizing portion 27 andcentral portion 25. Returning to FIG. 2, electrode 28 is smaller thancentral portion 25 and does not extend to interface 27A.

Stabilizing portion 27 may have a thickness from, for example, about 0.5nm to 5 nm, although thinner and thicker portions are suitable. Thethickness of stabilizing portion 27 is a function of the material ofstabilizing portion, and may be a function of any or all of the materialof ferromagnetic central portion 25, the dimensions of central portion25, and the thickness of the overall free layer 22. The thickness in theradial direction of stabilizing portion 27 is sufficiently thick toprovide exchange coupling with central portion 25, yet thin enough thatstabilizing portion 27 does not pin the magnetization orientation ofcentral portion 25 in a certain direction. For example, when stabilizingportion 27 is Pt₁₀Mn₉₀, a thickness of about 2 to 6 nm is suitable.

Stabilizing portion 27 stabilizes the remnant state of the magnetizationconfiguration of free layer 22 via exchange coupling, particularly, ofthe magnetization proximate interface 27A. Additionally, due to pinningat interface 27A, the magnetization within central portion 25 is morestable from its center to edge. This improves the thermal stability ofcell 20 and, when magnetic tunnel junction cell 20 is combined with aplurality of cells in a memory array, the exchange coupling at interface27A helps each individual free layer 22 maintain a single magnetizationorientation, and thus, helps cell 20 maintain its domain state.

Stabilizing portion 27 additionally improves the ability ofthermal-assisted writing. During writing, writing current passingthrough magnetic tunnel junction cell 20 heats up the stack to above theblocking temperature of the surrounding antiferromagnetic (AFM) material(for example, above 150° C. for Pt₁₀Mn₉₀). Above the blockingtemperature, the amount of exchange coupling reduces, allowing centralferromagnetic portion 25 to rotate. When the magnetization orientationof central portion 25 is reversed and the write current is removed,central portion 25 and the surrounding antiferromagnetic stabilizingportion 27 are cooled down, and thus the exchange coupling between themis recovered. When cooled, the magnetization orientation of centralportion 25 is stable. The resulting magnetization orientation is reverseto prior writing. As antiferromagnetic stabilizing portion 27 has no netmoment, it does not contribute to either noise in read back or producestray field to other adjacent magnetic tunnel junction cells.

FIG. 3 illustrates an alternate embodiment of a magnetic tunnel junctioncell that has the magnetization orientations of the free layer and thepinned layer perpendicular to the plane of the layers, or out-of-plane.Similar to magnetic tunnel junction cell 20 of FIG. 2, magnetic tunneljunction cell 30 of FIG. 3 has free layer 32 and a ferromagneticreference (i.e., pinned) layer 34 separated by an oxide barrier layer 33or non-magnetic tunnel barrier. A first electrode 38 is in electricalcontact with free layer 32 and a second electrode 39 is in electricalcontact with pinned layer 34. This illustrated tunnel junction cell 30does not include a pinning layer, however, in some embodiments a pinninglayer may be present. In FIG. 3, the magnetization orientations of freelayer 32 and pinned layer 34 are shown as in the same direction,although it is well understood that these orientations could beopposite.

Other layers, such as seed or capping layers, are not depicted forclarity. The various elements of cell 30 are similar to the elements ofcell 20, described above, except that the magnetization orientations oflayers 32, 34 are oriented perpendicular to the layer extension ratherthan in the layer plane.

In accordance with this disclosure, free layer 32 has a ferromagneticcentral portion 35 and a stabilizing portion 37 positioned radiallyproximate to central portion 35. In this embodiment, stabilizing portion37 is an antiferromagnetic material. Central portion 35 and stabilizingportion 37 meet at an interface 37A. In this embodiment, withstabilizing portion 37 being an antiferromagnetic material, exchangecoupling occurs at interface 37A between stabilizing portion 37 andcentral portion 35.

FIGS. 4 and 5 provide additional embodiments of magnetic tunnel junctioncells having a stabilization portion in the free layer, but in theseembodiments, the stabilization portion is a ferromagnetic material. FIG.4 provides a magnetic tunnel junction 40 wherein the magnetizationorientations of the free layer and the pinned layer are in-plane, andFIG. 5 provides a magnetic tunnel junction 50 having magnetizationorientations out-of-plane.

Returning to FIG. 4, magnetic tunnel junction cell 40 includes a softferromagnetic free layer 42, a ferromagnetic reference (i.e., pinned)layer 44, and an antiferromagnetic pinning layer 46. Free layer 42 andferromagnetic pinned layer 44, each which have a magnetizationorientation associated therewith, are separated by an oxide barrierlayer 43 or non-magnetic tunnel barrier. The magnetization orientationof pinned layer 44 is pinned by antiferromagnetic pinning layer 46, orin other embodiments, may be a fixed layer without pinning but with ahigh coercivity to stabilize itself. Note that other layers, such asseed or capping layers, are not depicted for clarity. A first electrode48 is in electrical contact with free layer 42 and a second electrode 49is in electrical contact with ferromagnetic pinned layer 44 viaantiferromagnetic pinning layer 46.

Free layer 42 has a ferromagnetic central portion 45 and a stabilizingportion 47 radially proximate central portion 45; in this embodiment,stabilizing portion 47 is a ferromagnetic material. Materials suitablefor stabilizing portion 47 include those suitable for central portion45; the material of stabilizing portion 47 may be the same material ordifferent than that of central portion 45. Central portion 45 has asmaller size (e.g., diameter) than the corresponding pinned layer 44;together, central portion 45 and stabilizing portion 47 have the same orsimilar size as the corresponding pinned layer 44. Separatingstabilizing portion 47 from central portion 45 is a spacer 41. Spacer 41is a non-magnetic material, in some embodiments, an electricallyconductive metal or an electrically insulating material. Examples ofmaterials suitable for spacer 41 include metals such as Cu and Ru andoxides such as AlO_(x) (e.g., Al₂O₃) and SiO₂. Spacer 41 has a thicknesssufficient to inhibit direct magnetic interaction between centralportion 45 and stabilizing portion 47; suitable thicknesses for spacer41 include those greater than 0.5 nm. As illustrated in FIG. 4A, centralportion 45 and spacer 41 meeting at an interface 45A, and stabilizingportion 47 and spacer 41 meet at an interface 47A. In this embodiment,with stabilizing portion 47 being a ferromagnetic material,magnetostatic coupling occurs across spacer 41 between stabilizingportion 47 and central portion 45.

Similar to described above in reference to magnetic tunnel junction cell20, stabilizing portion 47 stabilizes the remnant state of themagnetization configuration of free layer 42, in this embodiment though,via magnetostatic coupling across spacer 41.

Similarly in FIG. 5, magnetic tunnel junction cell 50 has free layer 52and a ferromagnetic reference (i.e., pinned) layer 54 separated by anoxide barrier layer 53 or non-magnetic tunnel barrier. A first electrode58 is in electrical contact with free layer 52 and a second electrode 59is in electrical contact with pinned layer 54. This tunnel junction cell50 does not include a pinning layer for setting the magnetizationorientation of pinned layer 54. Other layers, such as seed or cappinglayers, are not depicted for clarity. The various elements of cell 50are similar to the elements of cell 40, described above, except that themagnetization orientations of layers 52, 54 are oriented perpendicularto the layer extension rather than in the layer plane.

Free layer 52 has a ferromagnetic central portion 55 and a radiallyproximate stabilizing portion 57, which in this embodiment, is aferromagnetic material. Materials suitable for stabilizing portion 57include those suitable for central portion 55; the material ofstabilizing portion 57 may be the same material or different than thatof central portion 55. Separating stabilizing portion 57 from centralportion 55 is a spacer 51. In this embodiment, with stabilizing portion57 being a ferromagnetic material, magnetostatic coupling occurs acrossspacer 51 between stabilizing portion 57 and central portion 55.

Additional embodiments of magnetic tunnel junction cells having a freelayer with a stabilizing portion are illustrated in FIGS. 6 and 7. FIG.6 provides a magnetic tunnel junction 60 wherein the free layer islarger than the pinned layer, and FIG. 7 provides a magnetic tunneljunction 70 having the pinned layer larger than the free layer. Both ofthese cells 60, 70 are illustrated as having their magnetizationorientation in-plane and with no spacer material between theferromagnetic portion and an antiferromagnetic stabilizing portion. Itis understood that the features of these cells 60, 70 could be appliedto out-of-plane cells and to cells having ferromagnetic stabilizingportions and spacers.

Magnetic tunnel junction cell 60 includes a soft ferromagnetic freelayer 62, a ferromagnetic reference (i.e., pinned) layer 64, and anantiferromagnetic pinning layer 66. Free layer 62 and ferromagneticpinned layer 64 are separated by an oxide barrier layer 63 ornon-magnetic tunnel barrier. The magnetization orientation of pinnedlayer 64 is pinned by antiferromagnetic pinning layer 66. A firstelectrode 68 is in electrical contact with free layer 62 and a secondelectrode 69 is in electrical contact with ferromagnetic pinned layer 64via pinning layer 66. Free layer 62 has a ferromagnetic central portion65 and a radially proximate stabilizing portion 67.

Free layer 62 is larger than pinned layer 64, so that a portion of freelayer 62 overhangs pinned layer 64. In the illustrated embodiment,central portion 65 of free layer 62 approximately the same size aspinned layer 64, although in other embodiments, central portion 65 maybe larger or smaller than pinned layer 64. Stabilizing portion 67overhangs pinned layer 64 and other layers of cell 60.

Magnetic tunnel junction cell 70 of FIG. 7 includes a soft ferromagneticfree layer 72, a ferromagnetic reference (i.e., pinned) layer 74, and anantiferromagnetic pinning layer 76. Free layer 72 and ferromagneticpinned layer 74 are separated by an oxide barrier layer 73 ornon-magnetic tunnel barrier. The magnetization orientation of pinnedlayer 74 is pinned by antiferromagnetic pinning layer 76. A firstelectrode 78 is in electrical contact with free layer 72 and a secondelectrode 79 is in electrical contact with pinned layer 74 via pinninglayer 76. Free layer 72 has a ferromagnetic central portion 75 and aradially proximate stabilizing portion 77.

Pinned layer 74 is larger than free layer 72, so that a portion ofpinned layer 74 extends past free layer 72. In the illustratedembodiment, pinning layer 76 also extends past free layer 72, butbarrier layer 73 is present only between free layer 72 and pinned layer74.

Various embodiments of magnetic tunnel junction cells having a freelayer with a ferromagnetic portion and a stabilizing portion have beendescribed above. It is understood that numerous alternatives can be madeto the illustrated cells. For example, although FIGS. 2A and 4Aillustrate free layer 22, 42 as circular, these and their respectivecells 20, 40 may have other shapes, such as elliptical, oval, etc.Depending on the shape of the free layer, the thickness of thestabilizing portion may vary around the central ferromagnetic portion.As another example, only one layer (e.g., free layer 22, 32, 42, etc.)has been illustrated in the previous embodiments as having a stabilizingportion. In other embodiments, a stabilizing portion could be includedin another layer, for example, a pinned layer or pinning layer, inaddition to the free layer.

Referring to FIGS. 8A through 8G, a process for manufacturing a magnetictunnel junction cell having a free layer with a ferromagnetic portionand a stabilizing portion is illustrated. The resulting particularmagnetic tunnel junction cell is similar to cell 40 of FIG. 4, having aferromagnetic stabilizing portion separated from the centralferromagnetic portion by a spacer.

In FIG. 8A, a base stack that includes the various layers (i.e., bottomelectrode 89, pinning layer 86, pinned layer 84, barrier layer 83 andfree layer 82) is formed by well-known thin film techniques such aschemical vapor deposition (CVD), physical vapor deposition (PVD), oratomic layer deposition (ALD). At this stage, free layer 82 has a sizesimilar to the other layers; that is, at this step, free layer 82 is aprecursor to the eventual central ferromagnetic portion, as free layer82 does not have a reduced size.

In FIG. 8B, free layer 82 is patterned (e.g., a portion of free layer 82is removed) so that free layer 82 has a smaller size than thecorresponding pinned layer 84. Barrier layer 83 is an etch-stop, so thatbarrier layer 83 and pinned layer 84 are not etched.

Over the patterned free layer 82, in FIG. 8C, is deposited a thin spacerlayer 81, for example, by atomic layer deposition (ALD), that followsthe contours of free layer 82 and barrier 83. Over spacer layer 81 isthen deposited the stabilization material 87, in this embodiment,ferromagnetic material. If stabilization material 87 is anantiferromagnetic material, no spacer layer would be needed.

In FIG. 8D, stabilization material 87 is patterned to form a ring havinga size (e.g., diameter) the same as pinned layer 84. Over this patternedstabilization material 87 is deposited a dielectric material 90 in FIG.8E to cap the stack of layers and isolate the resulting magnetic tunneljunction cell from adjacent cells. In FIG. 8F, the surface is polished,for example by chemical mechanical polishing (CMP), to level dielectric90, stabilization material 87 and spacer 81 with free layer 82.

A top electrode 89 is deposited, FIG. 8G over free layer 82. Topelectrode 89 is narrower than free layer 82 to inhibit (preferablyprevent) current from flowing from electrode 89 to stabilizationmaterial 87. This resulting magnetic tunnel junction cell 80 is similarto magnetic tunnel junction cell 40.

FIG. 9 is a flow diagram of another method to manufacture a magnetictunnel junction cell having a free layer with a ferromagnetic portionand a stabilizing portion. Method 100 of FIG. 9 has an initial Step 101of forming the layers of the stack, the layers being the bottomelectrode, the pinning layer, the pinned layer, barrier layer and aferromagnetic free layer precursor. After being formed, the free layerprecursor is patterned in Step 102 to provide the free layer; thebarrier layer acts as an etch stop. Over the patterned free layer isdeposited a spacer layer, in Step 103. If the stabilizing material is anantiferromagnetic material, as in Step 103A, then the spacer layer isnot necessary. The stabilizing material is deposited over the spacerlayer. If the stabilizing material is an antiferromagnetic material, thespacer layer is not required. In Step 104, the stabilizing material ispatterned to form a stabilizing ring around the free layer. The stack iscovered (e.g., backfilled) with deposited dielectric material in Step105. The surface of the dielectric material, stabilizing material andspacer layer are polished in Step 106 to expose the free layer. The topelectrode is deposited and patterned in the final Step 107.

It is understood that the various other magnetic tunnel junction cells(e.g., cells, 20, 30, 50, 60, 70) could be made by methods similar tothose of FIGS. 8A through 8G and FIG. 9.

The magnetic tunnel junction cells of this disclosure may be used toconstruct a memory device that includes multiple magnetic tunneljunction cells connected together via word lines and bit lines, where adata bit is stored in the magnetic tunnel junction by changing therelative magnetization state of the ferromagnetic free layer withrespect to the pinned layer. The stored data bit can be read out bymeasuring the resistance of the magnetic tunnel junction cell, whichchanges with the magnetization direction of the free layer relative tothe pinned layer.

Thus, embodiments of the MAGNETIC MEMORY CELL CONSTRUCTION aredisclosed. The implementations described above and other implementationsare within the scope of the following claims. One skilled in the artwill appreciate that the present disclosure can be practiced withembodiments other than those disclosed. The disclosed embodiments arepresented for purposes of illustration and not limitation, and thepresent invention is limited only by the claims that follow.

1. A magnetic tunnel junction cell comprising: a free layer, aferromagnetic pinned layer, and a barrier layer therebetween, the freelayer comprising a central ferromagnetic portion having a first diameterand a stabilizing portion radially proximate the central ferromagneticportion; and an electrode having a second diameter, and being inelectrical contact with the free layer, wherein the second diameter issmaller than the first diameter.
 2. The magnetic tunnel junction cell ofclaim 1 wherein the stabilizing portion is an antiferromagneticmaterial.
 3. The magnetic tunnel junction cell of claim 2, whereinstabilizing portion stabilizes the central ferromagnetic portion byexchange coupling.
 4. The magnetic tunnel junction cell of claim 2wherein the stabilizing portion has a radial thickness of about 2-6 nm.5. The magnetic tunnel junction cell of claim 1 further comprising anelectrically insulating spacer between the central ferromagnetic portionand the stabilizing portion, the stabilizing portion being aferromagnetic material.
 6. The magnetic tunnel junction cell of claim 5,wherein stabilizing portion stabilizes the central ferromagnetic portionby magnetostatic coupling.
 7. The magnetic tunnel junction cell of claim1 wherein the central ferromagnetic portion has an in-planemagnetization orientation and the pinned layer has an in-planemagnetization orientation.
 8. The magnetic tunnel junction cell of claim7 further comprising an antiferromagnetic pinning layer proximate thepinned layer.
 9. The magnetic tunnel junction cell of claim 1 whereinthe central ferromagnetic portion has an out-of-plane magnetizationorientation and the pinned layer has an out-of-plane magnetizationorientation.
 10. A magnetic tunnel junction cell comprising: a freelayer, a ferromagnetic pinned layer, and a barrier layer therebetween,the free layer comprising a central ferromagnetic portion having a firstdiameter, the central ferromagnetic portion being magneticallystabilized by magnetostatic coupling or by exchange coupling from aradial direction; and an electrode having a second diameter, and beingin electrical contact with the free layer, wherein the second diameteris smaller than the first diameter.
 11. The magnetic tunnel junctioncell of claim 10 wherein the central ferromagnetic portion ismagnetically stabilized by magnetostatic coupling from a radiallypositioned ferromagnetic layer.
 12. The magnetic tunnel junction cell ofclaim 11 further comprising an electrically insulating spacer betweenthe central ferromagnetic portion and the radially positionedferromagnetic layer.
 13. The magnetic tunnel junction cell of claim 10wherein the central ferromagnetic portion is magnetically stabilized byexchange coupling from a radially positioned antiferromagnetic layer.